Shirred cellulosic casing for use in making a variety of sausage type products is well known in the art. Briefly, such casing is provided in the form of "sticks". A shirred casing stick is a hollow tube composed of a long length of casing which has been shirred and longitudinally compacted to greatly shorten its length. The reduction of casing length is defined by the ratio of the total casing length to the stick length, hereafter called "pack ratio". Thus, a one foot stick with a pack ratio of one hundred contains one hundred feet of casing. Shirring methods and apparatus are conventional and well known in the art.
A preferred embodiment of the present invention pertains to so called "small size" unreinforced cellulosic casing having an inflated diameter of about two inches and less. These small size casings are conventionally used in the production of frankfurter size sausages.
It also is known in the art to apply various coatings such as flavor enhancers or food colors to these small size casings prior to shirring. These coatings contain constituents which impregnate the casing so that after the casing is stuffed, a desirable characteristic is transferred to the food within the casing.
Such transfer may occur gradually over time or rapidly during processing, such as by cooking, so the product retains the characteristics of the additives even after the casing is removed. For example, if liquid smoke is applied to the casing, the food product within the casing will take on the fragrance, color, and taste of wood smoke without actually being subjected to a time consuming smoke house process. Liquid smoke compositions and casing articles coated with such compositions are more fully disclosed in U.S. Pat. Nos. 4,377,187; 4,446,167; 4,431,033; 4,525,397 and 4,540,613 and in Australian Pat. No. 151,768 among others.
Coating a small size casing with liquid smoke causes shirring problems. In particular, it is difficult to make a shirred stick having the desirable characteristics of a substantially straight bore, a high pack ratio, resistance to breakage, a smooth and unblemished appearance, and little or no "rope" (as defined hereinbelow). Aside from the shirring difficulties, meat packers prefer not to use shirred sticks which, based on appearance alone, appear to be defective. Accordingly, even though meat packers might benefit from using small size casing impregnated with liquid smoke, such use has been limited.
Difficulties in making a functionally and asthetically acceptable shirred stick of liquid smoke coated casing are thought to derive from the relatively high molecular weight constituents in liquid smoke and, in particular, from the liquid smoke constituents having a molecular weight greater than about 500.
These high molecular weight constituents are thought to block the interstices between the cellulose molecules and thereby impede the ability of the cellulose to take up water from the shirring solutions conventionally applied during shirring. The cellulosic structure of the casing is extremely hydrophillic. Normally, water is taken up so rapidly by the cellulose during shirring that a humectant is used to retard the uptake of water (see for example U.S. Pat. No. 3,981,046).
The water prevented from entering the interstices collects and remains at the surface of the casing. This surface water prevents a tight nesting relationship of the pleats formed during shirring and thereby lowers the resistance of the stick to breakage.
Resistance to breakage or "coherency" is important in that it is a measurement of the ability of the stick to maintain its structural and mechanical integrity so as to resist breakage when subjected to the rigors of manual handling or handling by automatic stuffing apparatus. Coherency is beam bending strength measured in inch-pounds and is derived in part from the geometry of the pleats formed by the shirring operation. These pleats are conical and nested one within another. The nested cone configuration and the surface friction of the pleats pressing one against the other are thought to contribute to the coherency of the stick.
However, if the water is prevented from entering the interstices between the cellulose molecules and instead collects and remains at the surface of the casing pleats, the cone shaped pleats are prevented from nesting tightly together. While the water at the pleat surface is eventually taken up by the casing over time, the coherency, once reduced, is only partly restored.
The wall of the cellulose casing is only about 0.001 inch thick and this thickness is not uniform about the casing circumference. It is well known in the art that this causes a shirred and subsequently longitudinally compressed stick to bow after doffing from the shirring/compressing mandrel. It also is suspected that the thinner part of the casing wall absorbs less water than the thicker parts and that this aggrevates bowing of the shirred sticks. Bowed sticks are not acceptable because they do not have a substantially straight cylindrical bore and therefore are not suited for automatic loading over a stuffing horn.
A coating of liquid smoke aggravates this problem and an uneven coating aggravates the problem still further. Depending upon the uniformity of the liquid smoke coating, one part of the casing may take up water more rapidly than another. This tends to swell the casing at different rates to produce a stick which is so excessively bowed that it is not suitable even for manual handling.
To a large extent, defects in the casing and other factors resulting in bowed sticks are negated by the known expedient of continuously twisting the stick during shirring. See for example, U.S. Pat. Nos. 3,454,981; 3,704,483. Conventional shirring, using shirring rolls of the type generally described in U.S. Pat. No. 3,461,484 gathers the casing into pleats that follow a continuous major pleat helix along the stick. Twisting the stick radially displaces one pleat from another and in this way distributes the irregularities and defects evenly about the stick so as to produce a stick which is straighter than a stick with no twist.
However, as pointed out in U.S. Pat. No. 3,454,981, twisting a stick in a conventional manner tends to produce a stick which is less coherent than a stick produced without twisting. Accordingly, twisting, which heretofore was a necessity, is not a completely acceptable solution to the problem. This is because a stick having a liquid smoke coating already has a coherency lower than a stick which does not have such a coating, and twisting the stick will lower coherency even further.
A further drawback of twisting is that the procedure magnifies any blemish in the coated casing. Harmless blemishes, such as a gradation in the color of the liqud smoke, extend longitudinally along the casing. Twisting the casing, as it is shirred, carries the blemish around the stick to produce a visible spiral or "barber pole" effect. Accordingly, an insignificant color variation which ordinarily would not be noticed, becomes most prominent when the casing is twisted. While this blemish usually will not hinder use of the casing, some meat packers will equate an imperfectly looking stick with a defective stick and will resist using it.
Another effect of twisting is a so called "rope appearance". Rope results when casing irregularities are carried around the shirring mandrel and is manifest by a wavy outer stick surface having the appearance of braided rope. The rope appearance usually does not detract from the use of the stick.
In summary, meat packers prefer to use a liquid smoke treated stick which has a uniform color and a smooth outer surface and which is free of visual blemishes. They will resist using a stick which does not have a uniform appearance and is not aesthetically pleasing even though the stick possesses the other desirable attributes of a straight bore, high pack ratio and high coherency.
Thus, an object of the invention is to provide a shirred stick of liquid smoke impregnated casing which has the desirable attributes of uniform color, a smooth outer surface free of visual blemishes, a coherency sufficient to permit handling by manual or automatic means, a substantially straight cylindrical bore so that the stick can be automatically loaded onto a stuffing horn which extends through the bore, and which has a pack ratio comparable to conventional shirred stick of clear casing.